1. Field of the Invention
The present invention relates to an image scanner, and more particularly, to a flat-bed image scanner.
2. Description of the Related Art
Conventionally, use has been made of various types of flat-bed image scanners for reading out images carried by documents, books and the like. In a flat-bed scanner, an image-carrying document to be read out is placed on a transparent supporting panel. Under the supporting panel, a movable image-reading unit (or carriage) is provided for scanning the document in a secondary scanning direction. FIGS. 9 and 10 of the accompanying drawings show two different types of conventional flat-bed image scanners.
Specifically, FIG. 9 illustrates a conventional image scanner which is provided with a document-supporting glass panel 1 and a carriage 2 arranged under the glass panel 1. The carriage 2 is arranged to move with respect to the glass panel 1 in the secondary scanning direction (indicated by a two-headed arrow).
As illustrated, a light source 3, a focusing lens 4, a line sensor 5 and a plurality of mirrors 6a-6c are all incorporated in the carriage 2. The mirrors 6a-6c are disposed so that the light path extending from an image-reading line L to the focusing lens 4 is rendered long enough.
With such an arrangement, the components 3-5 and 6a-6c held in the carriage 2 will be moved together (i.e., without changing their relative positional relationship) during an image-reading operation. Thus, the length of the above-mentioned light path is kept constant even when the carriage 2 is shifted in the secondary scanning direction. Also, the image-carrying light reflected on the document can accurately be led to the line sensor 5 since the positional relationship between the components 3-5 and 6a-6c is fixed.
FIG. 10 shows a second example of conventional image scanner including a first carriage 2a and a second carriage 2b. The first carriage 2a incorporates a light source 3 and a first mirror 6a, while the second carriage 6b incorporates a second and a third mirrors 6b, 6c. The illustrated image scanner also includes a focusing lens 4 and a line sensor 5 both of which are positionally fixed to the scanner.
When an image-reading operation is performed in the second conventional image scanner, the first carriage 2a is moved through a distance twice as great as a distance through which the second carriage 2b is moved. In this manner, the overall length of the light path extending from an image-reading line L to the focusing lens 4 is kept constant.
The two conventional image scanners described above have been found disadvantageous in the following points.
According to the arrangements shown in FIG. 9, the optical system of the scanner is collectively incorporated in the carriage 2. Thus, in order to lengthen the light path (extending from the image-reading line L to the focusing lens 4) for increasing the depth of focus of the optical system, the carriage 2 will disadvantageously become greater in size.
According to the arrangements shown in FIG. 10, the two carriages 2a, 2b need to be moved at different rates for maintaining the constant length of the light path, as stated above. Thus, a driving mechanism for actuating the carriages 2a, 2b will inevitably become complicated, which is disadvantageous in producing the image scanner.
It is, therefore, an object of the present invention is to provide an image scanner which eliminates or reduces the above-described problems.
According to the present invention, there is provided an image scanner comprising:
a housing provided with a first and a second side portions which are spaced from each other in a predetermined direction;
a document supporting panel fixed to the housing;
a carriage which is arranged under the document supporting panel and movable in said predetermined direction;
a light source supported by the carriage for illuminating a document placed on the document supporting panel;
first reflecting means supported by the carriage for directing light from the document toward the first side portion of the housing;
second reflecting means arranged at the first side portion of the housing for directing light from the first reflecting means toward the second side portion of the housing;
third reflecting means arranged at the second side portion of the housing for directing light from the second reflecting means toward the first side portion of the housing;
a focusing lens supported by the carriage for converging light from the third reflecting means; and
a line sensor supported by the carriage for receiving the converged light.
According to a preferred embodiment, the first reflecting means comprises a first mirror, the second reflecting means comprises a second and a third mirrors, and the third reflecting means comprises a fourth and a fifth mirrors.
These mirrors may be replaced with a suitable number of prisms.
According to the preferred embodiment, the first mirror is arranged to direct light to the second mirror, the second mirror being arranged to direct light to the third mirror, the third mirror being arranged to direct light to the fourth mirror, the fourth mirror being arranged to direct light to the fifth mirror, the fifth mirror being arranged to direct light to the focusing lens.
The focusing lens may have an optical axis extending through the line sensor.
In the preferred embodiment, the second mirror is arranged under the third mirror, the fourth mirror being arranged above the fifth mirror.
Alternatively, the second mirror may be arranged above the third mirror, while the fourth mirror may be arranged under the fifth mirror.
According to another preferred embodiment, the image scanner may further comprise additional reflecting means mounted on the carriage for conducting the light converged by the focusing lens to the line sensor.
In the above instance, the additional reflecting means may comprise at least one additional mirror.
Preferably, the additional reflecting means may comprise two additional mirrors. One of the additional mirrors may be arranged adjacent to the focusing lens, while the other of the additional mirrors may be arranged adjacent to the line sensor.
In a preferred embodiment, the, focusing lens and the line sensor may be offset from each other in a direction perpendicular to said predetermined direction.
In the above instance, said one of the additional mirrors may be spaced from the focusing lens in said predetermined direction, while said the other of the additional mirrors may be spaced from the line sensor in said predetermined direction.
Preferably, the image scanner of the present invention may further comprise driving means provided in the housing for reciprocating the carriage in said predetermined direction.
The driving means may include a pair of racks fixed to the housing, a pair of pinions which are rotatably supported by the carriage and held in engagement with the racks, a motor mounted on the carriage for rotating the pinions, and a speed-reduction mechanism mounted on the carriage and associated with the pinions and the motor.
Advantageously, the housing may include a cover member and a base member separate from the cover member.
Preferably, the third and the fourth mirrors may be attached to the cover member, while the second and the fifth mirrors may be attached to the base member.
Preferably, the light source may comprise a cold-cathode tube or a xenon lamp.
Preferably, the line sensor may: be provided with red, green and blue light-receiving elements for detecting color images.
Other objects, features and advantages of the present invention will become clearer from the detailed description of preferred embodiments given below with reference to the accompanying drawings.